The present invention relates to a new bifunctional alkyl phosphine oxide and a production method thereof. In particular, the present invention relates to a new bifunctional alkyl phosphine oxide which is useful for imparting flame retardant properties and antistatic properties and the like to fibers, plastics and the like.
Fibers, plastics and the like are required to have high functionality such as flame retardant properties, resin modifying properties, and antistatic properties. Bis(carboxyethyl)methyl phosphine oxide derived from an organophosphorus compound such as methyl phosphine has been used for these purposes. It is disclosed in U.S. Pat. No. 4,127,566 that polyesters wherein this compound is co-polymerized show good flame retardant properties. This polyester copolymer, however, has such drawbacks as a markedly lowered melting point and a somewhat low heat resistance.
In addition, methyl phosphine, which is to be used as a raw material, is in gaseous form at ordinary temperatures and under ordinary pressures, and can thus easily ignite and explode when contacted with air. Therefore, it is a very dangerous and hard-to handle substance. Moreover, it also is highly toxic, as well. Accordingly, it is desired that a monoalkyl phosphine which can be easily handled and which has low toxicity be provided.
Recently a method of producing a phosphine oxide represented by the general formula (5) which is used as a raw material monomer for a flame-resistant polyester copolymer has been disclosed (Japanese Patent Laid-Open Hei 6-166692, Japanese Patent Laid-Open Hei 6-166693), ##STR2## wherein, L represents an alkyl group, aryl group, aralkyl group, or a saturated alicyclic compound, M represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and N represents a hydrogen atom or methyl group.
According to the above-mentioned production method, the phosphine oxide is synthesized by reacting a primary phosphine and acrylonitrile, carrying out purification by distillation, followed by oxidation with hydrogen peroxide and hydrolysis with an alkali, or it is synthesized in a different order, that is, by carrying out the hydrolysis with an alkali, followed by oxidation with hydrogen peroxide. These methods, however, have such drawbacks that the synthesis requires a long process, and it is difficult to separate the product from the ammonium chloride which is generated in large amounts as a by-product during the hydrolysis. Thus, a product of high purity is hard to obtain. Though the publication discloses a compound of formula (5) wherein L is butyl, this compound is not described in the examples. As a matter of fact, the compound wherein L is t-butyl or 1,1,3,3-tetramethylbutyl cannot be produced in a method similar to the above-mentioned prior art technique (see following Comparative Example 1). The monophenyl phosphine disclosed in the example as an illustrative example of the primary phosphine, is hard to obtain, and the price is high.
In addition, illustrative compounds and synthesis methods according to the present invention are not disclosed at all in the publications.
In view of the above-mentioned facts, the present inventors carried out an intensive study of a bifunctional alkyl phosphine oxide as the functional organophosphorus compound, and identified a new bifunctional alkyl phosphine oxide.
The present inventors also found that a new bifunctional alkyl phosphine oxide of high purity can be produced in high yields, by carrying out reaction of a monoalkyl phosphine with (meth)acrylic acid or an ester thereof in the presence of an acid catalyst, and by adding an oxidizing agent to the resulting mixture to carry out the reaction, to thereby complete the present invention.